Method and a press cylinder device for producing a hollow body

ABSTRACT

The invention relates to a flow-forming method and device for producing a hollow article having a steplike shoulder from a tubular workpiece. For this purpose on the tubular workpiece is formed a conical area, which is selectively heated. Then an axial upsetting force is exerted on the workpiece, so that the heated conical area is upset and formed to the steplike shoulder. Both the shaping of the conical area and the upsetting can be performed on one flow-forming device.

[0001] The invention relates to a method for producing a hollow article, particularly a hollow shaft, with at least one step like shoulder from a tubular workpiece according to the preamble of claim 1. The invention also relates to a flow-forming device according to the preamble of claim 7.

[0002] Such a flow-forming device comprises a spindle drivable in rotary manner, a retaining device fitted thereto for the non-rotary retention of a tubular workpiece on the spindle, a spinning mandrel with an outer contour adapted to an inner contour of the workpiece and a tail stock, which is axially adjustable relative to the spindle.

[0003] A method of the related art is described in FR 2 481 273. According to this known method, the ends of a tubular workpiece are heated to forging temperature. Afterwards, conical areas are formed at the tube ends of the rotating workpiece by the infeeding of friction or roller tools. By the radial infeeding of additional, specifically shaped friction or roller tools, the inclination angle of the conical areas is increased until steplike shoulders and journals have been formed.

[0004] A device of the related art can e.g. be gathered from DE 195 11 963 A1. In this case a tubular starting workpiece is fixed in a flow-forming machine and radially drawn in by the radial infeeding of a spinning roller. This method is particularly efficient for simple parts. On radially drawing in a section of the tubular starting workpiece, steplike shoulders with radially directed walls are formed. These radially directed walls can under certain circumstances be exposed to strong forming forces, which on the one hand lead to a thinning of walls and on the other to material embrittlement and incipient cracks on exceeding the forming capacity.

[0005] A similar problem can arise in the method for producing a shaft according to DE 197 25 453 A1. In this known method for weight reduction reasons the shaft is constructed as a hollow shaft, which has steplike shoulders. During operation relatively high loads can occur on the steplike shoulders of hollow shafts and require a correspondingly thick dimensioning of the entire hollow shaft wall. However, this is contrary to the need for a lightweight shaft with a low mass moment of inertia.

[0006] The object of the invention is to give a method and a device with which it is possible to produce a hollow article, particularly a hollow shaft, with a steplike shoulder in an economic, weight-saving manner and at the same time high strength is ensured in the vicinity of the steplike shoulder.

[0007] This object is achieved by a method having the features of claim 1 and by a flow-forming device having the features of claim 7. Preferred embodiments of the invention are given in the dependent claims.

[0008] On the tubular workpiece a conical area is formed, which links a first workpiece section with a larger diameter to a second workpiece section with a smaller diameter, the conical area is selectively heated, an axial upsetting force is exerted on the workpiece and the heated conical area is upset and formed into the steplike shoulder. As a result of the axial upsetting the tubular starting workpiece collapses selectively in the heated conical area and as a result of the material obtained during upsetting, a steplike shoulder with a high wall thickness and therefore considerable strength is formed. As a result of the selective heating in the conical area the material of the workpiece is influenced in such a way that it is plastically deformable with respect to adjacent workpiece areas when a desired axial force is applied. This ensures that even with relatively long workpieces upsetting only occurs in the desired workpiece area. Heating can be brought about by a heating device or by friction as a result of engaging spinning rollers In the latter case, due to the three-dimensional stress state produced by the spinning rollers, a relatively limited heating is adequate for upsetting and wall thickening.

[0009] Fundamentally for the method according to the invention any tubular workpiece can be used, which is e.g. manufactured by casting or forging. A particularly reliable construction of the conical area is achieved in an embodiment of the invention in that the conical area of the tubular workpiece is constructed by flow-forming in a flow-forming machine. Thus, a planned wall thickness reduction in the conical area can for instance be obtained where, during upsetting, the workpiece bends in in a clearly defined manner.

[0010] According to a preferred further development of the invention, the heating and axial upsetting of the conical area is performed in the flow-forming machine in the same setting as the flow-forming. This allows a particularly economic manufacture of the desired cylindrical hollow article.

[0011] During axial upsetting the shape of the steplike shoulder can be developed freely, without the additional action of tools. If a particularly precise contour of the steplike shoulder is desired, it is advantageous according to the invention that during axial upsetting and during the shaping of the steplike shoulder the workpiece rotates and the shaping of the steplike shoulder takes place under the action of at least one spinning roller. Said spinning roller can be a sizing roller, which precisely predetermines the contour of the desired shoulder.

[0012] According to a further development of the invention, it is preferable during the shaping of the steplike shoulder to form in planned manner a wall thickness increase on the shoulder. This can in particular be brought about in that on the inside of the hollow article the material obtained on upsetting freely forms a material bead.

[0013] However, if a precisely defined inner contour is desired in the hollow article, according to the invention during the shaping of the steplike shoulder a mandrel is introduced into the workpiece and predetermines an inner contour of the shoulder. This inner contour can be a cylindrical shape with a rectangular shoulder for receiving a bearing. In this variant with a precisely predetermined inner contour, preferably a material bead is provided on the outside of the hollow article, which during a subsequent metal cutting machining operation, can be worked e.g. for forming a bearing seat. Thus, it is reliably ensured that even during a subsequent machining operation, an adequately large wall thickness and high strength are available in the stepped area.

[0014] Preferably, according to the invention, several steplike shoulders are formed on a workpiece. First of all, for this purpose the individual steps can be formed successively, the first conical area being heated first and then immediately following this the associated step is formed. These operations are repeated until all the shoulders have been formed. In another variant the different conical areas can be simultaneously heated and then the shoulders are formed in a single, common upsetting process.

[0015] Starting from a flow-forming device according to the preamble, the object is inventively achieved in that a mechanism is provided for the selective heating of a workpiece area and that the tail stock is constructed for exerting an axial upsetting force on the workpiece. With the flow-forming device according to the invention, it is possible for the previously described method to be performed in a single setting on a flow-forming machine.

[0016] On the flow-forming device a suitable mechanism can be provided for heating the workpiece and can be constituted by an induction device, a heat radiating means, a laser, a burner, etc.

[0017] According to a preferred embodiment of the invention, the spinning mandrel is placed on the tail stock and on the latter is formed a stop member for the transfer of the upsetting force. It is possible to set the spinning mandrel on the tail stock initially for adjusting the wall thickness of the work-piece and for forming the conical area by flow-forming in the same or opposite directions. Subsequently by moving the tail stock by means of a stop member on the latter an axial compressive force can be exerted on the workpiece in order to form the desired step system. The spinning mandrel can also remain within the workpiece, so as to ensure a clearly defined inner contour during upsetting.

[0018] In preferred manner this embodiment is further developed in that the spinning mandrel has at its free end a draw-in mandrel section, which is located on the spinning mandrel forming a steplike collar, which serves as a stop. In said device, after setting the wall thickness of the workpiece and forming the conical area, said mandrel is extended with the exception of the draw-in mandrel section from the tubular workpiece. Then, with a spinning roller the free end of the workpiece is drawn in against the draw-in mandrel section, the workpiece diameter being reduced at the drawn-in section. Thus, the free workpiece end faces the stop, so that by axially infeeding the tail stock, the desired upsetting force for forming the steplike shoulder can be transferred.

[0019] According to the invention, a particularly efficient working of the workpiece is brought about in that the retaining device has a driving tooth system, in which the workpiece can be axially shaped for producing a non-rotary connection. After pre-centring on the mandrel, the workpiece is pressed by the tail stock and/or the spinning roller under a high axial force against the driving tooth system, the workpiece being shaped into the driving tooth system accompanied by the formation of a non-rotary connection.

[0020] The invention is described in greater detail hereinafter relative to preferred embodiments and the attached diagrammatic drawings, wherein show:

[0021]FIG. 1 Diagrammatic cross-sectional views of a workpiece worked according to the invention in different working stages, and FIG. 2 Diagrammatic cross-sectional views of a workpiece fixed in a flow-forming device according to the invention in different working stages.

[0022]FIG. 1a shows a tubular workpiece 10 centrically positioned on a spinning mandrel 50. The spinning mandrel 50, which is part of a flow-forming device, has a first cylindrical area 54 and a second cylindrical area 56 having a smaller diameter, said two areas being interconnected by a conical area 52.

[0023] By axial and/or radial infeeding of at least one spinning roller 40, a desired outer contour of the workpiece 10 is set in contrarotating flow-forming To obtain the shape shown in FIG. 1b the spinning roller 40 is axially infed to the rotary workpiece 10 and, corresponding to an angle of entry on the spinning roller 40, the diameter is reduced and the workpiece is simultaneously axially lengthened. With a clearly defined setting of the forming parameters, particularly the compressive force and the rotary speed, contrarotating flow-forming by the roller can be performed spaced from the mandrel 5Q. The different diameter areas according to sections d1 and d2 in FIG. 1b are brought about by modifying said forming parameters and/or the radial infeed position of the spinning roller 40. The diameter areas d3 and d4 are achieved by a known ironing flow-forming, in which the spinning roller 40 forms the material directly cooperating with the spinning mandrel 50. In the present embodiment a conical area 12 is shaped with a clearly defined wall thickness, which links a first, larger diameter workpiece section 14 and a second, smaller diameter workpiece section 16.

[0024] Subsequently a diagrammatically represented mechanism 44 is infed at the conical area 12 and as a result the latter is selectively heated. Preferably a workpiece temperature in this area is set which is above the recrystallization temperature, so that the subsequent upsetting process can take place selectively in said area and without work hardening.

[0025] The axial upsetting process in which a force F is exerted on the workpiece 10 is illustrated in FIG. 1c. Through the axial force F the conical area 12 is telescoped, accompanied by the formation of a steplike shoulder 20. To obtain a clearly defined outer contour, use is made of a sizing roll 42 with a corresponding steplike contour, as can be gathered in detail from FIG. 1d. The upsetting process leads to the production of material, which leads to a wall thickness increase 22 in the vicinity of the steplike shoulder 20

[0026] For setting a clearly defined inner contour, as can be gathered from the upper half of FIG. 1c, the spinning mandrel is slid into the workpiece 10. Alternatively and according to the lower half of FIG. 1c, with an internally unsupported workpiece 10 a material head 24 can be formed, which ensures an additional material reinforcement on the inside of the workpiece 10.

[0027] The thus formed hollow article with the steplike shoulder 20 is shown in FIG. 1e. Said hollow article can optionally be provided with a further, steplike shoulder, where initially according to FIG. 1b a further conical area 32 is formed by a correspondingly shaped draw-in roller. This further conical area 32 can then be formed in accordance with the previously described method steps by heating and axial upsetting to give the further steplike shoulder. Thus, in an efficient and highly precise manner a hollow shaft with an undercut can be produced, a particularly pronounced material accumulation occurring at the corresponding steplike shoulders.

[0028] An alternative method performance and a device according to the invention are shown in FIGS. 2a to 2 d. A tubular workpiece 10 a with a solid base area 11 and a centring bore made therein, is axially pressed against a driving tooth system 64 of a retaining device 62 by three diagrammatically indicated multipurpose spinning rollers 46, which have a clearly defined mutual offset in the circumferential, radial and axial directions in known manner. The retaining device 62 is linked in non-rotary manner with a spindle 60 of a flow-forming device, whose fundamental construction with respect to the frame, drive and mounting support of the spinning rollers is known from the prior art. Between the spindle 60 and the retaining device 62 is provided a resiliently and axially displaceably mounted centring pin 61, which for the central mounting of the workpiece 10 a engages in its centring opening.

[0029] According to FIG. 2a, with the multipurpose spinning roller 46 a lengthening of the workpiece 10a by contrarotating flow-forming is firstly brought about. The thus produced intermediate product is shown in FIG. 2b. At this time the multipurpose spinning roller 46 is reset at the free end of workpiece 10 a and simultaneously there is a tilting of the roller by a tilt angle of e.g. 20°. By adjusting the multipurpose spinning roller 46, the bead-like projecting draw-in section 48 instead of the entry area 47 used during contrarotating flow-forming now engages on the workpiece 10 a.

[0030] According to FIG. 2c a spinning mandrel 50 a inserted in the workpiece 10 a during the contrarotating flow-forming is largely extended out of the workpiece 10 a, so that only a cylindrical draw-in section 72 located at the free end of the spinning mandrel 50 a remains in the workpiece 10 a. The draw-in section 72 has a smaller diameter than the cylindrical spinning mandrel 50 a and a clearly defined collar 74 is formed. This collar 74 serves as an axial stop through which on the one hand it is possible to limit an axial lengthening of the workpiece 10 a and on the other an axial upsetting force can be transferred to the workpiece 10 a by a tail stock of the spinning mandrel 50 a.

[0031] Through the bead-like draw-in section 48 of the multipurpose spinning roller 46, the free end of the workpiece 10 a is forced radially inwards against the cylindrical draw-in mandrel section and a conical area 12 a is formed on the workpiece 10 a. In accordance with the description of the method relative to FIG. 2, said conical area 12 a can be shaped to a steplike shoulder. For further shaping operations the multipurpose spinning roller 46, which is tilted by an angle a compared with contrarotating flow-forming, is moved along the outer circumference of the workpiece 10 a in fundamentally known manner. 

1. Method for producing a hollow article, particularly a hollow shaft, with at least one steplike shoulder (20) from a tubular workpiece (10), in which the tubular workpiece (40) is mounted on a drivable spindle (60) and is rotated, on the tubular workpiece (10) is formed a conical area (12), which links a first workpiece section (14) having a larger diameter with a second workpiece section (16) having a smaller diameter, and the conical area (12) is formed to the steplike shoulder (20), charakterized in that after forming of the conical area (12), it is selectively heated, by means of a tailstock an axial upsetting force is exerted on the workpiece (10) and the heated concial area (12) is pushed together by the axial upsetting force exerted by the tail stock and under the simultaneous action of at least one spinning roller (42) is formed to the steplike shoulder (20), the spinning roller (42) defining the contour of the desired shoulder (20) .
 2. Method according to claim 1, characterized in that the conical area (12) of the tubular workpiece (10) as produced by flow-forming in a flow-forming machine.
 3. Method according to claim 2, characterized in that the heating and axial upsetting of the conical area (12) in the flow-forming machine is performed in the same setting as the flow-forming.
 4. Method according to one of the claims 1 to 3, characterized in that a wall thickness increase is formed selectively on the steplike shoulder (20) during the shaping of the latter.
 5. Method according to one of the claims 1 to 4, characterized in that during the shaping of the steplike shoulder (20) a mandrel (50) is introduced into the workpiece (10) and predetermines an inner contour of the shoulder (20).
 6. Method according to one of the claims 1 to 5, characterized in that several steplike shoulders (20) are formed on a workpiece (10).
 7. Flow-forming device, particularly for forming a hollow article according to one of the claims 1 to 6, having a spindle (60) drivable in rotary manner, a retaining device (62) fitted thereto for the non-rotary retention of a tubular workpiece (10) on the spindle (60), a spinning mandrel (50) with an outer contour adapted to an inner contour of the workpiece (10) and a tail stock, which is axially adjustable relative to the spindle (60), Characterized in that a mechanism (44) is provided for the selective heating of a workpiece area and the tail stock is constructed for exerting an axial upsetting force on the workpiece.
 8. Flow-forming device according to claim 7, characterized in that the spinning mandrel (50) is located on the tail stock and a stop member for transferring the upsetting force is provided on the tail stock.
 9. Flow-forming device according to claim 7 or 8, characterized in that at its free end the spinning mandrel (50) has a draw-in mandrel section (72), which is located on the spinning mandrel (50) accompanied by the formation of a steplike shoulder (74) serving as a stop.
 10. Flow-forming device according to one of the claims 7 to 9, characterized in that the retaining device (62) has a driving tooth system (64), in which can be axially formed the workpiece (10) for producing a non-rotary connection. 